A key sheet is a component constituting a handy mobile equipment such as a portable phone, personal digital assistant (PDA) or the like, and a plurality of key tops working as push buttons each indicating an alphabetical and/or numerical key or a function key are adhered in an arrayed manner to the surface of a single sheet referred to as a key pad. The above-mentioned key pad is a flexible sheet having rubber elasticity such as a silicone rubber, thermoplastic elastomer or the like. On the undersurface of the key sheet thus configured, a printed circuit board provided with a plurality of normally open contacts closed by pressing a push button is closely disposed, so that push button switches are formed, and further a light source for illuminating a key top from the back surface is disposed.
Since the key sheet is thus configured in a state where a plurality of components are piled up in a layered manner, the thicknesses of each one of components are accumulated to have substantial thickness. Therefore, it is requested that the whole handy mobile equipment should be thinned as much as possible so as to further enhance the portability thereof.
However, for example in the method disclosed in Patent Publication 1, each component to be piled up has a conventional common configuration, which puts a structural limit on further thinner configuration. Moreover, there is a limit for the thinning of a key sheet only by using an EL sheet which is thinner than an LED as a light source.
Patent Reference 1
Japanese Laid-Open Patent [Kokai] Publication No. 2002-050258